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Published December 2007 | Published
Journal Article Open

The soft X-ray properties of AGN from the CJF sample: A correlation analysis between soft X-ray and VLBI properties


Context. We present the soft X-ray properties obtained in the ROSAT All-Sky survey and from pointed PSPC observations for the AGN in the complete flux-density limited Caltech-Jodrell Bank flat spectrum sample (hereafter CJF). CJF is a VLBI survey (VLBA observations at 5 GHz) of 293 AGN with detailed information on jet component motion. Aims. We investigate and discuss the soft X-ray properties of this AGN sample and examine the correlations between X-ray and VLBI properties, test beaming scenarios, and search for the discriminating properties between the sub-samples detected and not detected by ROSAT. Methods. Comparing the observed and the predicted X-ray fluxes by assuming an Inverse Compton (IC) origin for the observed X-rays, we compute the beaming or Doppler factor, δ_(IC), for the CJF sources and compare it with the equipartition Doppler factor, δ_(EQ). We further contrast the Doppler factors with other beaming indicators derived from the VLBI observations, such as the value of the expansion velocity, and the observed and intrinsic brightness temperature. We calculate two different core dominance parameters (R): the ratio of total VLBI flux to single-dish flux, R_V, and the ratio of the VLBI core-component flux to single-dish flux, R_C. In addition, we investigate the large-scale radio structure of the AGN and the difference between the pc- and kpc-scale structure (misalignment) with regard to the X-ray observations. Results. We find a nearly linear relation between X-ray and radio luminosities, and a similar but less stringent behaviour for the relation between optical and X-ray luminosities. The CJF-quasars show faster apparent motions and larger values of δ_(IC) than the radio galaxies do. The quasars detected by ROSAT have a different β_(app)-redshift relationship compared to the non-detected ones. We find no significant difference in R between the quasars detected and not detected by ROSAT. We find evidence that R is larger for quasars and BL Lac objects than it is for radio galaxies, in accordance with unification scenarios. ROSAT-detected sources tend to reveal extended large-scale radio structures more often. Conclusions. We conclude that beaming alone cannot explain the observed dichotomy of ROSAT detection or non-detection and assume that the large-scale jet structure plays a decisive role.

Additional Information

© ESO 2007. Received 26 November 2004. Accepted 2 October 2007. We wish to thank A. Witzel and T. P. Krichbaum for thought-provoking discussions and many useful comments. The ROSAT project is supported by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) and the Max-Planck-Gesellschaft. Part of this work was supported by the European Commission, TMR Programme, Research Network Contract ERBFMRXCT97-0034 CERES and by the DLR, project 50QD0101. S. Britzen acknowledges support by the Claussen-Simon Stiftung. This research has made use of the NASA/IPAC Extragalactic Data Base (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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